Modern agricultural practices rely heavily on precise and timely applications of fertilizers, herbicides, pesticides and other chemicals. In situations where the applications must be made to standing row crops, such as corn or beans, liquid or granular materials are often applied using a high ground clearance, self-propelled applicator.
In order to provide maximum ground clearance, such applicators utilize highly specialized suspension systems for connecting the ground engaging wheels of the applicator to a frame of the applicator. Typically, separate hydraulic drive motors are provided as part of the suspension, for each drive wheel, to thereby further enhance ground clearance by minimizing the encroachment of drive line or typical suspension components into the space between the wheels under the applicator.
In the past, suspension systems for high ground clearance, self-propelled applicators utilized suspension components, including compression springs and hydraulic shock absorbers, that were essentially the same as those used in automotive and commercial vehicle suspensions. While these components have generally worked well in the specialized suspension systems of high ground clearance, self-propelled applicators, they are not ideal and further improvement is desirable.
One problem with prior high clearance applicator suspension systems, is that the ground clearance tends to vary depending upon how heavily the applicator is loaded. Initially, as it pulls away from a tender with a full load, an applicator is typically carrying several thousand pounds of a product to be applied. As the product is dispensed onto the field by the applicator, the weight of the remaining product being carried by the applicator gradually decreases to zero. With prior suspensions that rely on compression springs for supporting the load carried by the applicator, ground clearance starts out at a minimum when the applicator is initially fully loaded, with the springs compressed to their lowest working height. As product is dispensed and load on the applicator decreases, the compression springs extend from their initially compressed state, and raise the applicator higher above the ground surface.
Having ground clearance vary is undesirable for at least two reasons. First, the effectiveness of the product being applied is highly dependent upon precise application. As ground clearance changes, spray or granular spreading patterns may be adversely affected, requiring continual compensating adjustments to be made by an operator of the applicator, in order to maintain optimal product application. Second, ride quality and handling characteristics of the applicator are typically affected by ground clearance, and the state of extension of the compression springs. The springs, and hence the suspension, is considerably stiffer when the springs are more fully compressed than when they are extended.
Prior suspension systems using compression springs are also typically optimized for one type of operating mode. This results in compromising suspension performance in other operating modes that are typically necessary in practical utilization of the applicator. For example, it is necessary to drive the applicator across the field in an unloaded state, to and from the tender, in addition to driving the vehicle across the field in a fully or partially loaded state while applying product to the field. It will likely be necessary for the applicator to travel on public roads, at times, in moving between fields. Differences in handling characteristics inherent in spring-based suspension systems, from loaded to unloaded states of the applicator, may make such on-road transit more difficult. It may be necessary to transport the applicator on a truck or trailer between fields. This can present additional problems for high ground clearance applicators, in that the overall combined height of the applicator and the bed of the trailer or vehicle carrying the applicator may exceed applicable limits for transport on public roads.
It is desirable, therefore, to provide an improved suspension system for self-propelled, high ground clearance, agricultural product applicators. It is particularly desirable to provide such an improved suspension system that can set and maintain a desired ground clearance, and provide desirable ride and handling characteristics in a self-propelled, high ground clearance, agricultural product applicator throughout a wide range of operating modes and conditions. It is also particularly desirable to provide a system for limiting speed, based on weight, for given tasks, to facilitate safe operation and provide increased reliability of the applicator.